The present invention relates in general to aquarium filtering devices which are typically disposed beneath the surface of the aquarium bed and more particularly to a filter cartridge which filters water which is sucked by a water pump from the space beneath the aquarium filter device and returned to the water contained in the aquarium.
Undergravel aquarium filters generally include a perforated plate or panel previous to water and supporting thereon a gravel bed and which is, in turn, supported in the aquarium tank in spaced relation with the bottom wall or floor of the aquarium. This plate defines with the aquarium bottom wall a chamber which receives water flowing through the gravel bed on the undergravel filter. The water collected in the chamber between the perforated panel and the bottom wall of the aquarium is drawn from that chamber, aerated and returned to the aquarium tank. In this manner the aquarium water is continually drawn through the gravel bed which filters the water and to some degree conditions the same due to the fact that bacteria settled on the gravel particles provide aerobic filtration of water. Thus, the typical underground filter provides for two of the three main methods of filtration, namely mechanical and biological filtration. It does not provide for chemical filtration.
The water flowing through the gravel bed and into the chamber between the perforated plate and the aquarium tank floor, must be circulated back into the aquarium tank. In one conventional method, a riser tube is connected leading from the chamber below the perforated plate which leads back to the water within the aquarium tank above the plate. An air pump is employed, which pumps air into the chamber below the riser tube. The air flows upwardly in the riser tube and generates a reduced pressure thereby causing the water to flow upwardly in the riser tube from the chamber and back into the aquarium tank above the plate. In addition, air bubbles produced by the air pump aerate the water which is returned into the tank. In this method both air and water flow up the riser tube and any restriction can cut down the flow of water in the riser tube.
In other conventional methods, so-called power heads are utilized for the water withdrawal from the chamber beneath the perforated plate. The power head is a water pump electrically driven for sucking water collected in the chamber formed between the plate and the bottom of the aquarium tank and causing it to flow upward in the riser tube and into the aquarium tank above the plate. One or more nozzles are mounted on the power head which faces the interior of the aquarium tank, to direct the water back into the tank.
U.S. Pat. No. 2,935,199 discloses a typical undergravel filtering device which comprises a flat perforated supporting plate spaced from the bottom of the aquarium tank and permitting water to pass therethrough but preventing the gravel from passing through its openings. An air tube is connected to an air pump to draw the water by generating air bubbles into the chamber. The water from the chamber between the supporting plate and the bottom wall of the aquarium tank flows up a riser tube which extends to the level of the water in the aquarium tank and conveys the water and air from that chamber back into the tank.
U.S. Pat. No. 3,199,678 shows a water treatment assembly for an undergravel filtering device, which comprises an air inlet tube and a riser tube retained in position by a collar and attached to a flat base mounted on the undergravel filtering device. When the water treatment assembly is in operation the air bubbles which enter the chamber beneath the undergravel filter through the air inlet tube will push or move the water upwardly into the riser tube. The water treatment assembly is situated in the riser tube and provides chemical filtration as the water passes through it. However, since both air and water flow up the riser tube, there is only a limited amount of chemical filtration that can be achieved since chemical filtration is dependent upon the amount of water turnover flowing through the chemical filter. Additionally, in the configuration shown, any small restriction in the riser tube cuts down the flow by as much as 75%. Thus even the chemical filter itself positioned in the riser tube acts to cut down the flow of water.
With all conventional undergravel filtering devices, however, small particles remain entrapped in the water after the latter has passed the gravel bed. Also, when using the power head for sucking the water up the riser tube there is a need for additional degassing and filtering of the water before it is returned to the aquarium tank. The filtration of the underground filter cannot provide for the chemical filtration thus, there is no way to remove the chlorine in a fish tank. Likewise, food dyes in the fish food cannot be removed. Urea and other by-products remain in the aquarium water and cause a yellowing of the aquarium water. Should medications be added for the elimination or prevention of fish diseases, these also remain in the water without being filtered.
Accordingly there is need for a reliable filtering device for chemical filtration of the aquarium water when using an underground filter. This is especially important when a power head is used whereby there is a great flow of water up the riser tube, which flow should not be restricted by the chemical filter.